9335 HYDROGRAPHIC MANUAL PaGE 852 



a. Symholization of rocks. — Rocks shall be symbolized on liydrographic sheets in 

 accordance with 7823, reefs and ledges in accordance with 7824, and other rocky areas 

 in accordance with 7826, and the elevations and notes accompanying them shall be 

 according to 7825. Adjustments between topographic and hydrographic data shall 

 be made in accordance with 7827. 



Without exception, where a sounding, surrounded by deeper water, reduces to 

 zero and the notation in the Records is "rky" or "on rock," the rock awash symbol (-)f ) 

 shall be used (see 78236) . For emphasis, a rock constituting a menace to navigation 

 may be symbolized by the rock awash symbol and accompanied by the notation "awash 

 at extreme low tides", even though not in accordance with 7823. 



The correct notation for a rocky bottom is "rky". Where the notation "Rk" or 

 "Rock," has been used in the Sounding Record, it should be interpreted as meaning 

 "rky", unless the surrounding depths are much greater than the sounding in question 

 or a special explanation is placed in the "Remarks" column, in which case "Rk" is to 

 be appended to the sounding. 



Where a cluster of rocks awash is contiguous to the shoreline and descriptive notes 

 are given for each rock, only those notes shall be inked that give the elevations of the 

 outermost rock and of the highest rock. Where the reef is a detached one, consisting of 

 numerous detached rocks, or is contmuous in character, the highest rock or point of 

 the reef should be described as well as such other rocks or points as the importance and 

 extent of the feature justify. 



The range of tide given in the report of the Division of Tides and Currents shall 

 be examined before being used to determine the heights of rocks, to make certain that 

 it is based on MHW (and not on MHHW). 



9335. Adjoining Surveys 



Where two surveys join or overlap, the soundings at the junction shall be trans- 

 ferred froih one of the hydrographic sheets to the other. The purposes of the transfer 

 are: (a) To permit a comparison to be made between the depths at the junctions. 

 Where different methods, such as echo sounding and leadhne sounding or three-point 

 sextant fixes and R.A.R. control, are used on two adjoining surveys, a defect in one of 

 the methods is strikingly disclosed from a study of the overlap. It also permits a 

 junction of the depth curves on the two surveys. (6) To insure that no holidays have 

 been left in the hydrography at the junctions, (c) To simplify chart construction. 



In effecting the transfers, the following practices shall be followed: 



In general, overlap shall be transferred from the smaller scale to the larger scale (e.g., from 

 1:40,000 to 1:20,000). This usually means the transfer of fewer soundings. 



In changeable areas, only hydrography from surveys of the same, the following, or the preceding 

 year, shaU be transferred. 



In unchangeable areas, contemporary surveys should always be transferred. Where there is no 

 contemporary survey, hydrography from prior surveys shall not be transferred except where the new 

 survey is a resumption of a previous project, or where the project instructions specify that a 

 satisfactory junction shall be made with a prior survey. In such cases the latest survey should show 

 whether such junction has been effected. 



Soundings on a sheet must not be obscured by soundings transferred from an adjoining sheet. 

 If a transferred sounding falls too close to a sounding already on the sheet, omit the former unless it 

 is an important shoal sounding, in which case it should be shown and the less important sounding 



